1. Field of the Invention
The invention relates to a fuel cell stack.
2. Description of the Related Art
Conventionally, fuel cell stacks employ a so-called circulation type fuel-gas passage structure for distributing fuel gas within the fuel cell stack. The circulation type fuel-gas passage structure is used to discharge nitrogen gas, which accumulates within a fuel-gas passage portion and interferes with the supply of fuel gas, to the outside of the fuel cell stack. The nitrogen gas enters the fuel-gas passage portion from an oxidizing-gas passage portion via the electrolyte. Meanwhile, a non-circulation type fuel-gas passage structure for fuel cell stacks has been proposed which is used with a nitrogen gas storage provided outside of the fuel cell stack and connected to the fuel cell stack via a valve, which is described in Japanese Patent Application Publication No. 2005-243476 (JP-A-2005-243476). According to this structure, fuel gas is supplied to the fuel cell stack while repeatedly switching the state of the valve between the open state and the closed state (non-continuous operation type fuel cell system). That is, when fuel gas is supplied to the fuel cell stack, the valve is closed, whereby the pressure in the fuel cell stack increases.
However, the above publication recites nothing regarding the possibility or the necessity to provide a fuel cell stack having a non-circulation type fuel-gas passage structure that allows continuous fuel cell operation.